1. Field of the Invention
The disclosures herein generally relate to an atomic oscillator, a method of detecting a CPT (Coherent Population Trapping) resonance and a magnetic sensor.
2. Description of the Related Art
An atomic clock (an atomic oscillator) is an extremely accurate clock. Technologies for reducing the size of the atomic clock are being studied. The atomic clock is an oscillator based on transition energy of an electron included in an atom of alkali metal or the like. Especially, electron transition energy of an alkali metal atom is found to be quite accurate if the process is not influenced by any disturbance. Accordingly, stability of frequency, which has been improved by more than several orders of magnitude compared with a crystal oscillator, can be obtained.
There have been several types of atomic oscillators. For example, an atomic oscillator having a structure of a microwave oscillator of the related art has a large size and requires large amount of electric power. On the other hand, a CPT (Coherent Population Trapping) type atomic oscillator provides stability of frequency, precision of which is higher by three orders of magnitude than that of the crystal oscillator of the related art. Furthermore, it is hoped that size and power consumption of the CPT type atomic oscillator can be reduced. A prototype of the CPT type atomic oscillator was manufactured in 2007, and products of the CPT type atomic oscillator have been sold by Symmetricom, Inc., U.S.A. since 2011.
U.S. Pat. No. 6,993,050 discloses a CPT detector and a method for detecting CPT. The CPT detector includes a quantum absorber, a polarization analyzer, and a detector. The quantum absorber includes a material having first and second low energy states coupled to a common high energy state. Transitions between the first low energy state and the common high energy state and between the second low energy state and the common high energy state are induced by electromagnetic radiation having a predetermined polarization state. The polarization analyzer blocks electromagnetic radiation of the predetermined polarization while passing electromagnetic radiation having a polarization state that is orthogonal to the predetermined polarization. The polarization analyzer is irradiated with a portion of the generated electromagnetic radiation that has passed through the quantum absorber. The detector generates a signal related to the intensity of electromagnetic radiation that leaves the polarization analyzer.
Japanese Published Patent Application No. 2010-263593 discloses an optical system of an atomic oscillator that regulates an oscillation frequency by using an optical absorption property by one of a double resonance method utilizing light and micro waves and a coherent population trapping (CPT) method utilizing a quantum interference effect produced by two kinds of resonance light. The optical system includes a light source emitting the resonance light; a gas cell disposed at an emitting side of the light source, sealing a gaseous metal atom therein and transmitting the resonance light through a metal atom gas; a light detecting unit detecting the transmitted light that is transmitted through the metal atom gas; and a fluorescence blocking unit blocking at least a part of fluorescence, which is emitted from the metal atom gas to the light detecting unit, and disposed between the metal atom gas and the light detecting unit.
Japanese Patent No. 4801044 discloses a method for modulating an atomic clock signal and a corresponding atomic clock. The laser beams (L1, L2) are pulse-modulated in amplitude to illuminate (A) an interactive medium. A detection (B) of the current pulse (Sr) and of the pulses (Sr-1 to Sr-p) preceding said current impulsion is performed. The pulses are superimposed (C) by linear combination to generate a compensated atomic clock signal (SHC) whereof the spectral width is minimized. The invention is applicable to atomic clocks with pulsed interrogation whereof the interactive medium consists of thermal or laser-cooled atoms.
P. M. Anisimov, et al., “Influence of transverse magnetic fields and depletion of working levels on the nonlinear resonance Faraday effect”, Journal of Experimental and Theoretical Physics, November 2003, Volume 97, Issue 5, pp 868-874 discloses the nonlinear resonance Faraday effect studied under the condition of coherent population trapping in 87Rb vapor at the D1-line F=2 to F′=1 transition. The influence of transverse magnetic fields on the nonlinear optical Faraday rotation is studied. For the transverse fields perpendicular to the electromagnetic-wave polarization, a simple theoretical model is proposed, which is in good agreement with experimental data. The optimal intensity providing the maximum sensitivity is found based on the results obtained. The influence of working-level depletion on the parameters of Faraday rotation in open systems is studied experimentally and theoretically. The system was closed in the experiment by using an additional laser to increase the sensitivity and extend the dynamic range of measured fields.
G. Kazakov, et al., “Pseudoresonance mechanism of all-optical frequency-standard operation”, Phys. Rev. A 72, 063408 (2005) proposes an approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of 10−14/√τ.
Data used in the present application are available at http://steck.us/alkalidata/ by D. A. Steck, Dec. 18, 2012.